I. Field of the Invention
This invention relates to a package containing an agent for retaining qualities of food products or the like.
II. Description of the Prior Art
Air-permeable packages containing agents for retaining qualities of food products or the like are conventionally used. The quality-retaining agents include oxygen absorbents, freshness-retaining agents, desiccants, insecticides and the like. Since the main use of these packages is to retain the qualities of food products, the packaging material should have the waterproofing properties, mechanical durability, and safety to the human body, on top of the air-permeability. In case of oxygen absorbent, the air-permeability of the packaging material should be precisely controlled according to the food product so as to obtain the best oxygen content for the food product.
Conventional packaging materials for packaging oxygen absorbents include laminates of a polyethylene film with through holes and a sheet of paper. The air-permeability of the material is controlled by the porosity, i.e., the percentage of the opening area in the total area of the material. However, the porosity is uncontrollably changed in the process of thermally adhering the polyethylene film onto the paper. Further, since the packaging material is not water-resistant, in case of applying the oxygen absorbent package to a moistened food, the packaging materials is dampened to reduce the air-permeability thereof and is also mechanically damaged. Still further, the oxygen absorbent in the package may permeate out of the package through the paper and the through holes in the polyethylene film to diffuse into the food, to threaten the safety and hygiene of the food.
An improved packaging material is disclosed in Japanese patent disclosure (Kokai) No. 53-51096. The disclosed material is a laminate of two plastic films with through holes having different melting points and a laminate further containing a sheet of paper disposed between the two plastic films. Similar materials are disclosed in Japanese patent disclosure (Kokai) No. 56-124440 and No. 56-124441. Although these materials have better water resistivity than paper-based materials, since they have a number of through holes, the content may permeate through the through holes, to bring about the problem on safety and hygiene, when they are applied to moistened food. Further, the mechanical strength of the material is low since a number of holes are formed in the material. The porosity of the material is uncontrollably changed in the process of adhering the two films.
Further, these packages ae obtained first as a belt-shaped linked package comprising the individual packages ranging in a row, and then the individual packages are separated from each other by cutting off the connecting portions between the individual packages. The separated packages are immediately placed in packages containing a food product or the like in situ. Since the belt-shaped linked package contains thousands of individual packages and the individual packages are cut off one by one at one end of the belt, considerable time has elapsed before the last individual package is placed in the food-containing package. Thus, before being placed in the food-containing package, the quality-retaining agent in the last individual package has already been used and hence has reduced its quality-retaining power.